Cytokinetic events that promote actomyosin ring constriction and septum formation

适当的细胞分裂对于生物体的生长、发育和存活至关重要。细胞分裂的缺陷与发育异常和各种疾病有关。细胞分裂的最后阶段是胞质分裂，其中两个子细胞在物理上分开。成功的胞质分裂需要在时间和空间上精确控制的多个步骤。这种精确调节的性质和分子细节知之甚少。该项目旨在了解如何精确控制这一复杂的多步骤过程，以确保成功的细胞分离。胞质分裂从酵母到哺乳动物在进化上是保守的，因此在酵母中学到的东西直接适用于哺乳动物（如人类）。研究细胞分裂和胞质分裂的最佳模型系统之一是裂殖酵母。使用分裂酵母模型系统的初步工作已经非常清楚地揭示了胞质分裂早期阶段的机制细节。解开分裂酵母胞质分裂的分子细节，将提供一个范例，研究类似的过程中复杂的生物体，并将导致更好地了解各种异常的病因与胞质分裂。胞质分裂是细胞分裂的最后一步，对所有细胞的生存和发育至关重要。胞质分裂是一个时间上有组织的多步骤过程，涉及一个细胞一分为二的物理分离。首先，一个肌动球蛋白环的形式，然后经历收缩同时与隔膜进入膜沟的形成。目前尚不清楚这些事件在时间上是如何组织的。在裂殖酵母中，隔膜的内移对于膜沟的形成至关重要。向内的隔膜提供了克服细胞内部膨压所需的力。目前尚不清楚肌动球蛋白环收缩和隔内移是如何同时发生的。没有肌动球蛋白环也能产生膜沟，那么肌动球蛋白环在胞质分裂中起什么作用呢？ 在瓣膜成型环组装后，短暂等待后发生瓣膜成型环收缩和隔膜内移。是什么触发了环收缩和隔膜形成？初步数据显示，后环组装，保守的GTdR Cdc 42被激活，在一个独特的时空方式。Cdc 42在胞质分裂过程中的激活模式取决于其激活子Gef 1和Scd 1的定位。 Gef 1促进在环处的隔膜合成蛋白的募集，以允许环收缩和隔膜内陷的及时发生，而Scd 1是正常隔膜形成所需的。Gef 1还促进均匀的环收缩和隔膜内移。基于这些数据，提出的中心假设是Cdc 42的时空激活使得组装的肌动球蛋白环能够充当适当的环收缩和隔膜形成的标志和指导。为了验证这一点，将追求以下目标：1。为了定义如何Cdc 42是时空激活的分裂网站后环组装; 2。为了确定如何环收缩和隔膜的形成是由Cdc 42的时空激活促进;和3.描述肌动球蛋白环如何作为对称环收缩和间隔形成的标志和引导。该项目将整合活细胞成像，蛋白质动力学分析，遗传学和数学建模。该项目将提供如何建立独特的Cdc 42激活模式的更深入的了解，导致在胞质分裂不同的功能，并将提供深入了解信号模式如何组织细胞中复杂的多步骤过程。该项目将在大多数真核生物胞质分裂的机制理解中产生广泛的影响。

Proper cell division is critical for growth, development, and survival of an organism. Defects in cell division have been linked to developmental anomalies and various afflictions. The final stage of cell division is cytokinesis, where the two daughter cells are physically partitioned. Successful cytokinesis requires multiple steps that are precisely controlled both in time and space. The nature and molecular details of this precise regulation is poorly understood. This project aims at understanding how this complex multi-step process is precisely controlled to ensure successful cell separation. Cytokinesis is evolutionarily conserved from yeast to mammals and hence what is learned in yeast is directly applicable to mammals (such as humans). One of the best model systems to study cell division and cytokinesis is the fission yeast. Preliminary work using the fission yeast model system has, with great clarity, revealed the mechanistic details of the early stages of cytokinesis. Unraveling the molecular details in cytokinesis in the fission yeast will provide a paradigm to study similar processes in complex organisms and will lead to a better understanding of the etiology of various anomolies related to cytokinesis. Cytokinesis, the final step in cell division, is central to survival and development of all cells. Cytokinesis is a temporally organized multistep process that involves the physical separation of a cell into two. First, an actomyosin ring forms, which then undergoes constriction concurrent with septum ingression for membrane furrow formation. It is not clear how these events are temporally organized. In fission yeast, septum ingression is critical for membrane furrow formation. The ingressing septum provides the force required to overcome internal turgor pressure in the cell. It is not clear how actomyosin ring constriction and septum ingression occur concurrently. Membrane furrowing can occur without an actomyosin ring so what role does the actomyosin ring play in cytokinesis? Ring constriction and septum ingression occurs after a short waiting period, post ring assembly. What triggers the onset of ring constriction and septum formation? Preliminary data shows that post-ring assembly, the conserved GTPase Cdc42 is activated in a unique spatiotemporal manner. Cdc42 activation pattern during cytokinesis depends on the localization of its activators, Gef1 and Scd1. Gef1 promotes the recruitment of a septum synthesizing protein at the ring to allow timely onset of ring constriction and septum ingression, while Scd1 is required for normal septum formation. Gef1 also promotes uniform ring constriction and septum ingression. Based on this data the proposed central hypothesis is that spatiotemporal activation of Cdc42 enables the assembled actomyosin ring to act as a landmark and guide for proper ring constriction and septum formation. To test this, the following aims will be pursued; 1. To define how Cdc42 is spatiotemporally activated at the division site post ring assembly; 2. To determine how ring constriction and septum formation is promoted by spatiotemporal activation of Cdc42; and 3. To describe how the actomyosin ring acts as a landmark and guide for symmetric ring constriction and septum formation. This project will integrate live cell imaging, analysis of protein dynamics, genetics, and mathematical modeling. This project will provide a deeper understanding of how unique Cdc42 activation patterns are established, leading to distinct functions in cytokinesis and will provide insights into how signaling patterns organize complex multistep processes in the cell. This project will have widespread implications in the mechanistic understating of cytokinesis in most eukaryotes.